In phase I, nine females and males were each placed into three groups of three and given a series of six intramuscular (IM) injections approximately 60 days between injections of CDB-1830 (levonorgestrel butanoate) at a low, medium and high dose for groups I through III respectively. Blood collections consisted of two pre-treatments followed by daily blood collections from days 1 to 7, then weekly thereafter until the next injection. Blood collections continued on a weekly basis following the sixth injection until the circulating levels of levonorgestrel (LNG) fell below 0.1 Ng/ml. In all of the dose groups of phase I, concentrations of serum lng following each subsequent injection had increased but were considerably lower than the response exhibited after the first injection. A retrospective analysis of serum testosterone was added to phase I males to determine whether testosterone production was suppressed by the presence of lng. Serum testosterone levels dropped following each injection of CDB-1830 in all groups and did not return to pre-treatment levels until 7, 10, and 14.5 Months for groups I to III respectively. In phase II, one group of three males and three females were given two intravenous (IV) injections and an IM injection of CDB-1830v (levonorgestrel butanoate) at 1 mg/ml, CDB-107c (levonorgestrel) at 0.817 Mg/ml and CDBb-1830 (levonorgestrel butanoate) at 1 mg/ml respectively. LNG levels were about twice as high following injection of CDB-107C then in CDB-1830v and at least ten fold lower following the IM injection in both the male and female groups. synthetic progestin